Residual soil phosphorus as the missing piece in the global phosphorus crisis puzzle

Abstract

Phosphorus (P) is a finite and dwindling resource. Debate focuses on current production and use of phosphate rock rather than on the amounts of P required in the future to feed the world. We applied a two-pool soil P model to reproduce historical continental crop P uptake as a function of P inputs from fertilizer and manure and to estimate P requirements for crop production in 2050. The key feature is the consideration of the role of residual soil P in crop production. Model simulations closely fit historical P uptake for all continents. Cumulative inputs of P fertilizer and manure for the period 1965-2007 in Europe (1,115 kg . ha(-1) of cropland) grossly exceeded the cumulative P uptake by crops (360 kg ha(-1)). Since the 1980s in much of Europe, P application rates have been reduced, and uptake continues to increase due to the supply of plant-available P from residual soil P pool. We estimate that between 2008 and 2050 a global cumulative P application of 700-790 kg . ha(-1) of cropland (in total 1,070-1,200 teragrams P) is required to achieve crop production according to the various Millennium Ecosystem Assessment scenarios [Alcamo J, Van Vuuren D, Cramer W (2006) Ecosystems and Human Well-Being: Scenarios, Vol 2, pp 279-354]. We estimate that average global P fertilizer use must change from the current 17.8 to 16.8-20.8 teragrams per year in 2050, which is up to 50% less than other estimates in the literature that ignore the role of residual soil P.

Fig. 1.

Scheme of the DPPS model. The model includes two dynamic pools of P: the labile (P_L) and the stable (P_S) pools, comprising both organic and inorganic P. Four inputs of P to the system are defined: fertilizer, manure, weathering, and deposition. The coefficient ρ refers to the total P input (mineral fertilizer and manure) after subtracting runoff loss. The coefficients f and 1 − f refer to the fraction of ρ that transfers to the P_L and P_S, respectively. Coefficient α represents the crop P uptake fraction from P_L. Parameters ω and δ are weathering and deposition inputs to the P_L and P_S, respectively. μ_LS and μ_SL denote to the transfer rate of P from the P_L to the P_S and from P_S to the P_L, respectively (redrawn from ref. 11).

Fig. 2.

Trends of annual P application and P uptake in cropland for the period 1965–2050 according to GO scenario in (A) Western Europe, (B) North America, (C) Africa, (D) Asia, (E) Latin America and (F) Oceania. Long-term FAO data (15) and simulation results are illustrated by circles and lines, respectively. Shaded and open circles refer to P application and P uptake rates, respectively. Dashed and solid lines refer to P application and P uptake rates, respectively. The regions are based on those defined by the FAO (15). The R² values for calculated vs. observed P uptake (1965–2007) range from 0.62 for Oceania, 0.81 for Western Europe, 0.83 for North America, 0.84 for Africa, 0.93 for Latin America, and 0.98 for Asia.

Fig. 3.

(A) Global annual applications of inorganic P fertilizer and manure P between 1965 and 2007. (B) Trends of annual P application and P uptake in cropland for the period 1965 to 2050 in the entire globe according to the four MEA scenarios. Long-term FAO data (15) and simulation results are illustrated by circles and lines, respectively. Shaded and open circles refer to P application and P uptake rates, respectively. Dashed and solid lines refer to P application and P uptake rates, respectively. The R² value for calculated versus observed P uptake (1965–2007) is 0.96.

Fig. 4.

(A) P recovery from actual historical data (1965–2007) and future simulated data (2008–2050). AF, Africa; N-A, North America; L-A, Latin America; AS, Asia; E-E, Eastern Europe; W-E, Western Europe; and OC, Oceania. (B) Global P recovery from 1965 to 2050.

Fig. 5.

Hysteresis in P uptake vs. P application between 1965 and 2007 (Western Europe). With the same amount of P application, there are two rates of P uptake that show the contribution of the residual P to the crop production.